1. Technical Field
The present disclosure generally relates to firearms. More specifically, the present disclosure relates to an annular piston system for rifles.
2. Description of Related Art
In the context of firearms, gas-operation is a system of operation that provides energy for auto-loading firearms. In gas-operation, a portion of high pressure gas from the cartridge being fired is used to power a mechanism to extract the spent casing and chamber a new cartridge. Energy from the gas is harnessed through either a port in the barrel or trap at the muzzle. This high-pressure gas impinges on a surface such as a piston head to provide motion for unlocking of the action, extraction and ejection of the spent casing, cocking of the hammer or striker, chambering of a fresh cartridge, and locking of the action.
Most current gas-operation systems employ some type of piston. The face of the piston is acted upon by gas from the combustion of the propellant from the barrel of the firearm. Traditional piston-based gas-operation system is a cylindrical piston that reciprocates on top of, by the side, or under the firearm barrel. Gas is introduced by a gas block that directs the gas to where the piston is located. These designs are generally simple and reliable. However, since the piston is off the center of the barrel, the piston-based gas-operation system tends to introduce a bending moment to the rifle upon firing, undesirably impairing the firearm's accuracy. On the other hand, direct gas impingement system largely keeps the moving parts co-centered with the rifle barrel, hence has better accuracy. However, such system tends to introduce hot gas directly into the firearm receiver. This thus undesirably subjects the firearm receiver under thermal stress and leaves fire powder foul inside the receiver, rendering the firearm more prone to jamming.
There are some historical firearms that have annular piston design. One is the World War II era Walther Mkb42(w) from Germany. This design uses an annular piston and a half circle sleeve to transfer momentum to the bolt carrier. This will lower the bending momentum to the barrel although not eliminating it completely. Due to the complication of manufacturing of this design, the MKb42(w) was less successful than the Haenel MKb42(h), a similar firearm but using a cylindrical piston system that resides on the top of the barrel. The Haenel MKb42(h) was later improved to be the legendary Stg44, the first so called “assault rifle.” Another example is the VZ52 from the former Czechoslovakia. It uses an annular piston and a half circle sleeve to transfer the momentum to the bolt carrier, just like the Walther MKb42(w). However, the sleeve and the bolt carrier are not locked to each other. This is what is called a “short stroke” piston system. Both of the aforementioned rifles have their main spring located in the rifle receiver or stock. As such it is very hard to make the total length of the rifle short.